Aircraft: COMMERCIAL FIXED WING
Phase of flight: Taxi
Anomaly: Deviation / Discrepancy - Procedural Published Material / Policy; Ground Event / Encounter Loss Of Aircraft Control

Uneventful approach and landing from ILS 03 approach. Light weight aircraft. We reported braking action good after landing rollout (first aircraft to land). Turn off runway at B5 was normal and completed after landing checklist. The B5 taxiway definitely looked slippery due to its reflectivity. ATIS was reporting 1/8 slush all taxiways. I fly this trip multiple times every month and I am very familiar with the slight downslope of the taxiway prior to the left turn onto the 60 ft wide taxiway H. I approached the left turn with extreme caution and the slowest possible speed; however as I initiated the turn onto H the aircraft only turned slightly off the B5 centerline before beginning to slide straight ahead. I was immediately aware that the aircraft was sliding and applied maximum break application when the aircraft did not turn. The slide continued approximately 20-40 feet before I was able to stop the aircraft with application of minimal idle reverse and the maximum brake application. I believe our light weight and residual thrust was a factor on a slight downslope surface that was contaminated with frozen slush. Relative to the runway and our ramp area it appeared that there was minimal sand applied to that taxiway intersection. Once stopped I set the parking brake. We stopped ON the taxiway surface and SLIGHTLY left of centerline; but unable to attempt another turn onto taxiway H. We advised tower of our predicament and informed them we would need to contact our ramp to coordinate a tow-in by Maintenance. Tower had no issue with our actions or need for assistance. The aircraft was towed to the gate with no further issues and there was no damage to the aircraft. I called the duty officer upon arrival at the ramp to relay the details of the required tow to the ramp. Our very experienced maintenance personnel reported to me that airport ops would have an interest in the occurrence. As it turned out; the duty officer called me back once I had arrived at the layover hotel to inform me that the Deputy Chief of Airport Ops wanted to get a statement from me. I called the Deputy Chief immediately and respectfully declined to make a written statement; but verbally provided the same details I have provided here. I respectfully directed him to re-contact the duty officer for direction to retrieve the data he wanted through our safety reporting system. I; again; called the duty officer to inform him of my polite interaction with [the deputy]. Duty Officer concurred with my decision not to provide written statement which was very helpful on his part. During my conversation with the Deputy Chief; I expressly complimented the Ops crew that provides a runway in very good condition for landing every morning in spite of the often foul weather conditions. In spite of doing all we could as a crew to analyze; brief and take action to mitigate what we knew to be the threat of taxiways in poor condition we as a crew and I; specifically as the Captain; was unable to execute a safe taxi to the ramp in icy conditions. Poor decision making; human error. Although I have operated this flight into Appleton many times and have taxied to the ramp in what I would consider conditions that were much worse than today; perhaps (in hindsight) I should have requested a tow-in before attempting the turn onto the 60 ft foot wide H taxiway. I believe the taxiway condition was worse than I realized and considerably worse than the reported 1/8 slush. 'Skating rink' would have been a better description. Today; we were lucky and remained on the taxiway surface. Air carrier Captain reported the aircraft slid on ice contaminated taxiway during taxi at ATW airport.